/Engine/Source/Runtime/Experimental/Chaos/Public/Chaos/SimCallbackObject.h
Called once in a simulation step if any particles were unregistered. Occurs immediately before UniqueIdxs become invalid.
virtual void OnParticleUnregistered_Internal &40; TArray< TTuple< Chaos::FUniqueIdx, FSingleParticlePhysicsProxy &42; >> & UnregisteredProxies &41;